Conventionally, there is a post-processing apparatus for carrying out a post-processing on a sheet conveyed from an image forming apparatus. The post-processing apparatus is equipped with a processing tray, a standby tray and a discharge tray. The processing tray carries out the post-processing. The standby tray is arranged at the upper part of the processing tray. The standby tray temporarily buffers succeeding sheets while the post-processing of a sheet is carried out by the processing tray. The standby tray drops a buffered sheet towards the processing tray if the processing tray is in a standby state. The discharge tray is arranged at a downstream side with respect to the processing tray in a sheet conveyance direction.
The post-processing apparatus controls a switch between a processing mode and a non-processing mode (normal mode). The processing mode carries out a post-processing on a sheet. In the processing mode, the sheet to which the post-processing is carried out by the processing tray is discharged to the discharge tray via the standby tray.
On the other hand, the non-processing mode conveys the sheet as it is without carrying out the post-processing on the sheet. In the non-processing mode, the sheet is discharged to the discharge tray via the standby tray and the processing tray. Otherwise, in the non-processing mode, the sheet is discharged to the discharge tray via another route, but not the processing tray. For example, a route passing through the standby tray but not the processing tray is included in another route. However, if the sheet passes through the processing tray or another route, since an extra step until the discharge of the sheet to the discharge tray is required, there is a possibility of inhibiting a processing speed of the post-processing apparatus.